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    pdiffy is a perceptual difference tool used to compare images for differences. This tool is primarily aimed at web developement for comparing different states of a website.

    Getting Started

    Install the module with: npm install pdiffy


    Run pdiffy server to start the interface and web server.

    You can run a schedule process that creates sessions at different intervals. Screen shots taken get embedded into the session file. The session can be imported into the interface. pdiffy may need to run with root permissions depending on where it is installed. PhantomJS writes to a directory where it is installed and the user would need write permissions.

    Run pdiffy [path] to run a job based on a config.

    Run pdiffy combine [sessions] -o [output] to combine multiple session files.

    This does not delete the original session files.

    Run pdiffy difference [paths | urls] -o [output] -t [threshold] -m [mode] to perform differences and output the file. Path can be a URL or path to an image file or any combination of the two.

    Job Options


    The path to the file you want to save to. Make sure node has permissions to write to this destination. This must have the extension .pdiffy in order for it to be able to be imorted into the interface.


    pdiffy uses node-schdule to schedule jobs. This uses the object literal syntax. Please refer to it's documentation. If the schedule is absent then the job occurs only once.


    Interval is similar to schedule except instead of schedule a time it executes every N minutes. If schedule and interval are present, schedule takes priority.


    Whether to add a timestamp to the filename. This is true by default when the schedule option is present.


    pdiffy uses node-webshot to take screen shots. These options are just passed through to node-webshot.

    These also can contain an object containing plugins.

    • Object options.plugins - keys are plugin names and values are a hash of parameters. Refer to the documentation in the plugins folder.
    • String options.mode - Mode to perform difference if one is being performed.
    • Boolean options.ignoreColors - Uses brightness to calculate difference other than RGB values.
    • Object options.tolerance - Object with value tolerances
      • Number red - Tolerance for red values
      • Number green - Tolerance for green values
      • Number blue - Tolerance for blue values
      • Number minBrightness - Tolerance for minimum brightness


    An array of captures. These contain the following parameters:

    • Object options - Overrides the global options
    • String|Array url - The url to capture or if an array or urls are passed those pages will be captured and a difference will be performed from each of them.

    Using Programmatically

    var pdiffy = require("pdiffy");



    Starts the server for the interface. Returns with a method killServer.

    capture(config, callback)
    • Object config - config object
    • Function callback - callback function

    Takes a config schedule object. This will only execute the capture once. Use runSchedule() when wanting to start a schedule.

    run(config, callback)
    • Object config - config object
    • Function callback - callback function

    Runs a job based on the config object.

    combine(sessionPaths, outputPath)
    • Array sessionPaths - array of session paths
    • String outputPath - path to write to disk

    Combine multiple session files.

    • Object options - config options
      • Array paths - Array of paths. Can be a URL or path to a file.
      • Object [captureOptions] - Options for capturing URLs.
      • Object [diffOptions] - Options for difference processing.
      • String [output] - Output path to a file. If no output is provided the callback will get passed the data.
      • Function [callback] - Function to receive data when an output is not provided.

    Takes an array of paths and performs a difference on them.


    Heres an example schedule file (json):

      "output": "path/to/session/file.pdiffy",
      "schedule": {
        "minutes": 30
      "options": {
        "shotSize": {
          "width": "all",
          "height": "all"
        "plugins": {
          "hideElements": {
            "selectors": ["#myId"]
      "captures": [
          "options": {},
          "url": ""
        }, {
          "options": {
            "tolerance": {
              "red": 50,
              "green": 16,
              "blue": 16
            "mode": "block"
          "url": ["", ""]
        }, {
          "options": {},
          "url": ""


    In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code using Grunt.


    Copyright (c) 2013 Steven Sojka. Licensed under the MIT license.`




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